Field of the Invention
The invention relates to a semiconductor component having a metal semiconductor junction, and in particular to a Schottky diode with a low leakage current. The semiconductor component has a metal semiconductor junction between a metal that acts as a first electrode and a semiconductor of a first conductivity type with a drift path.
In IGBT power modules, pn diodes are currently used as freerunning diodes. These diodes have low impedance and a low reverse current. The switching losses, caused by the high concentration of minority carriers in the drift path, are a disadvantage. With regard to the switching losses, Schottky diodes would be ideal, because only majority carriers participate in the current transport. In addition, the lesser forward voltage of only 0.3 to 0.4 V in Schottky diodes, compared with about 0.7 V in pn diodes, is also advantageous for the static losses. A disadvantage of Schottky diodes, however, is the extremely high on-state resistance, because the Schottky diode is a majority carrier component. The reverse current of a Schottky diode is also very high. The reverse current is caused by the so-called Schottky barrier lowering: The high field intensity applied to the metal semiconductor junction in the off-state lowers the Schottky barrier, the consequence of which is a corresponding rise in the reverse current. This is described, for instance, by S. M. Sze in Physics of Semiconductor Devices, New York, p. 252.
This typical situation for unipolar components, which is that the on-state voltage, adjusted via the doping, determines the off-state capability of a component also exists in MOSFETs. Commonly owned U.S. Pat. No. 5,438,215 (German 43 09 764) proposed that higher-doped zones of the opposite conductivity type from the drift zone be disposed in the region of the space charge zone, in order to reduce the on-state resistance of a MOSFET. Between these higher-doped zones are zones that have the conductivity type of the inner zone but higher doping.